These are usually called "near field probes". You can easily make a basic one yourself with a piece of thin coax [1]. As leoedin mentions, they are useless wit

These are usually called "near field probes". You can easily make a basic one yourself with a piece of thin coax [1]. As leoedin mentions, they are useless without some instrument to attach them to. Ideally a $100k+ spectrum analyzer, but you can sometimes get some basic readings out of them also with just a cheap oscilloscope + a RF detector [2]. [1] http://www.emcesd.com/tt120100.htm http://www.emcesd.com/tt120100.htm [2] https://www.aliexpress.com/item/32747667435.html https://www.aliexpress.com/item/32747667435.html